Filter device

ABSTRACT

A cleansing tank  38  and a screw conveyor  32  are removably mounted to a mounting opening  22  of a filtration tank  2 . When the cleansing tank  38  and the screw conveyor  32  are to be removed, they can be extracted to the exterior of the filtration tank  2 , by detaching a base  28 , which axially supports the screw conveyor  32 , from a rim  24 . Purified water is backwashed through a purified water discharge pipe  60  when the cleansing tank  38  and the screw conveyor  32  are extracted and inserted through the mounting opening  22 . This causes filtration media  14  to float, thereby reducing the resistance thereof.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a filtration apparatus forfiltering liquids such as water. Particularly, the present inventionrelates to a filtration apparatus, to the interior of which a filtrationmedia cleansing mechanism is mountable.

BACKGROUND ART

[0002] Conventionally, at large scale water treatment facilities such aswater purification plants, water purification processes are performedby: removing fine suspended matter by filtering water through a layer offiltration media such as filtration sand; then by disinfecting thefiltered water with chlorine. As cleansing methods of the filtrationmedia, surface cleansing, which washes the surface of a sand layer byhitting it with water sprayed from a nozzle, and backwash cleansing,which forces purified water into a filtration reservoir from a lowerpressure compartment, thereby floating the filtration sand grains,causing them to rub against each other, are in common use.

[0003] However, if the backwash cleansing is repeated over a long periodof time, the water pressure thereof influences even a gravel layer,creating areas of different thickness in said layer, which is optimallyflat and of an even thickness. In addition, the surface cleansing andbackwash cleansing methods cannot cleanse the filtration media withsatisfactory efficacy. Problems arise from repeated use over a period oftime such as contaminant accumulation on the filtration media. In thiscase, it is necessary to perform a regeneration process, which involves:totally ceasing the operation of the filtration reservoir, removing thefiltration media, cleansing the filtration media, and replacing thecontaminated filtration media, which has been cleansed. However, theregeneration process is extremely costly, and as during said process thefiltration reservoir is not operating, it leads to a decrease in watertreatment efficiency.

[0004] The applicant of the present invention, in order to meet thisdemand, has developed and proposed a sand cleansing apparatus whichcleanses polluted filtration media in a shorter time and with a higherdegree of cleansing ability (Japanese Unexamined Patent Publication Nos.10(1998)-109051 and 11 (1999)-057526). This sand cleansing apparatuscomprises: a sand receiving opening for receiving filtration media drawnfrom a filtration reservoir in its upper portion; a cleansing tank whichstores sand and cleansing water having a sand extraction opening; aagitation tank erected within said cleansing tank having openings on theupper and lower ends thereof; and a screw conveyor which rotates withinsaid agitation tank. The grains of sand are brought upward by the screwconveyor along with the cleansing water. As they are being conveyedupward, said grains of sand rub against each other by being agitated,and the scrubbing action thereof effectively removes the contaminantsthat are attached or coated thereon.

[0005] Filtration apparatuses, such as filtration tanks, which areinstalled in small scale simple plumbing networks or factories, differfrom the large scale water purification plant described above. It is notpractical to employ the sand cleansing apparatuses proposed by thepresent applicants (Japanese Unexamined Patent Publication Nos.10(1998)-109051 and 11(1999)-057526) in these filtration apparatuses.This is because the utilization scales of the filtration apparatuses aresmall. Therefore, it is not efficient to secure space to install thesand cleansing apparatus in, and to expend costs associated with theinstallation and removal of the sand cleansing apparatus, when comparedto the case of the filtration reservoir.

[0006] There are known filtration devices, as disclosed in JapanesePatent No. 31491 and Japanese Unexamined Utility Model Publication No.63(1988)-98704, which have been developed in view of these points. Thefiltration device disclosed in Japanese Patent No. 31491 comprises acentral pipe (cleansing tank), which is suspended by a frame (supportportion). The lower end of the central pipe opens within a filtrationchamber (filtration tank). A propeller is provided within the interiorof the central pipe, at its lower end. A pipe having a jet expulsionopening is provided above the propeller, the jet expulsion opening beingslightly above the upper edge of the central pipe. The pipe having thejet expulsion opening is linked to the propeller, and rotates therewith,to spray cleansing fluid in the horizontal direction by use ofcentrifugal force. During filtration, water having contaminants issupplied from above, and is filtered by passing through filtration sand,which is provided on an apertured false bottom (filtration floor).During cleansing, the propeller is rotated, causing filtration sand tobe suctioned into the central pipe via the lower opening thereof. Thefiltration sand is elevated through the central pipe, then discharged inthe horizontal direction by the cleansing fluid being sprayed from thejet expulsion opening. The filtration sand is cleansed by contaminantsbeing separated therefrom at this time.

[0007] The filtration device disclosed in Japanese Unexamined UtilityModel Publication No. 63-98704 comprises an elevating pipe (cleansingtank) erected therein, and a spiral water elevator provided within theelevating pipe. During filtration, water is discharged by a waterdispersing tube, which is within filtration sand. Processed water, whichhas been filtered by passing through the filtration sand from below, isdischarged above the filtration sand. During cleansing of the filtrationsand, the spiral water elevator rotates and elevates the filtrationsand, which has trapped contaminants, from the lower portion of thespiral water elevator. The contaminants are separated from thefiltration sand by use of centrifugal force. The filtration sand isexpelled through a filtration sand expulsion opening, which is providedin the upper portion of the elevating pipe.

[0008] Wear of the aforementioned propeller, central pipe, spiral waterelevator and the elevating pipe is unavoidable over long term use, dueto the relative movement among them and the filtration sand.Accordingly, the frequency of part replacement in the aforementioneddevices is high.

[0009] In the filtration device disclosed in Japanese Patent No. 31491,the frame, to which the central pipe (cleansing tank) for cleansing thefiltration media and the propeller is mounted, is suspended from aconduit pipe, which is provided at the upper portion of the filtrationtank. However, the central pipe has a diameter far greater than theframe, and it cannot be dismounted from the conduit pipe to the exteriorof the filtration tank. Accordingly, when the propeller or the centralpipe become worn by the filtration media, it becomes necessary todisassemble the filtration tank to remove the propeller and thecleansing tank. In addition, filtration cannot be sustained, becauseagitation of the filtration media by the propeller crushes thefiltration media (the properties of the filtration sand are changed).

[0010] In the filtration device disclosed in Japanese Unexamined UtilityModel Publication No. 63-98704, the spiral water elevator is provided inan elevating pipe, which is formed integrally with a expulsion spout,through which filtered water is expelled. However, the elevating pipe isnot configured to be removable from within a tank (filtration tank) Inaddition, the spiral water elevator is axially supported by smallopenings above and below it, and is also of a configuration that doesnot enable removal from within the tank. For these reasons, it isextremely difficult to exchange the elevating pipe and the spiral waterelevator.

SUMMARY OF THE INVENTION

[0011] The present invention has been developed in view of the pointsdescribed above. It is an object of the present invention to provide afiltration apparatus, in which a cleansing tank and a screw conveyor areeasily replaced, thereby facilitating maintenance thereof.

[0012] It is a further object of the present invention to provide a lowcost filtration apparatus, in view of the fact that filtrationapparatuses having cleansing mechanisms built in are expensive.

[0013] The filtration apparatus of the present invention is a filtrationapparatus for filtering liquid, which is introduced into a filtrationtank, and discharging filtered liquid to the exterior of the filtrationtank, comprising:

[0014] the filtration tank that houses filtration media; and

[0015] a filtration media cleansing mechanism that comprises a hollowcleansing tank for cleansing the filtration media; and a contaminantexpulsion means for expelling contaminants separated from the filtrationmedia to the exterior to the filtration tank; wherein:

[0016] the cleansing tank is a cylindrical body that hangs within thefiltration tank from the upper portion thereof;

[0017] the cleansing tank is provided with a lower opening at a positionlower than the upper surface of the filtration media housed in thefiltration tank, and a plurality of upper openings at a position higherthan the upper surface of the filtration media;

[0018] the cleansing tank is provided with a screw conveyor forconveying the filtration media and the liquid, which enter the cleansingtank from the filtration tank via the lower opening, upward from thelower opening to the upper openings while scrubbing the filtration mediawithin the cleansing tank;

[0019] a mounting opening, to which the upper portion of the cleansingtank is removably attachable, is provided at the upper portion of thefiltration tank; and

[0020] a cleansing portion, comprising the cleansing tank, the screwconveyor, and a drive mechanism for the screw conveyor, is removablyattachable to the filtration tank via the mounting opening, from theexterior of the filtration tank.

[0021] It is preferable that the cleansing portion is configured so thatthe lower end of the screw conveyor protrudes downward from the loweropening of the cleansing tank.

[0022] A configuration may be adopted, wherein:

[0023] the cleansing portion is constructed by a plurality of arts,which are detachably linked so as to separate in the axial direction ofthe screw conveyor.

[0024] A configuration may also be adopted, wherein:

[0025] slots that enable the filtration media to pass therethrough areformed at the lower portion of the cleansing tank so that at least aportion of the slots are below the upper surface of the filtrationmedia.

[0026] A configuration may further be adopted, wherein:

[0027] a plurality of gaps that extend along the outer periphery of theaxis of the screw conveyor are formed in the interior sides of theblades of the screw conveyor.

[0028] The filtration tank may be filled with the liquid to be filteredso that the liquid surface is at least at the upper openings of thecleansing tank.

[0029] The filtration apparatus of the present invention is also afiltration apparatus for filtering liquid, which is introduced into afiltration tank that houses filtration media, and discharges filteredliquid to the exterior of the filtration tank, wherein:

[0030] a mounting opening that the filtration media is visible throughis provided in the filtration tank above the filtration media;

[0031] a removably attachable lid is provided to cover the mountingopening; and

[0032] the lid is removed during cleansing of the filtration media, toinsert and fix a cleansing means in the mounting opening, the cleansingmeans comprising a hollow cleansing tank, a screw conveyor for conveyingthe filtration media and the liquid upward while scrubbing thefiltration media within the cleansing tank, and a drive mechanism forthe screw conveyor, to perform cleansing of the filtration media.

[0033] The filtration apparatus of the present invention comprises thefiltration tank, the hollow cleansing tank for cleansing the filtrationmedia within the filtration tank, and the filtration media cleansingmechanism. The cleansing tank is a cylindrical body, which is suspendedwithin the filtration tank from above. The screw conveyor, for conveyingthe filtration media and the liquid upward from the lower opening to theupper openings of the cleansing tank while scrubbing the filtrationmedia, is provided within the cleansing tank. The mounting opening, forremovably mounting the upper portion of the cleansing tank, is providedat the upper portion of the filtration tank. The cleansing portion,comprising the cleansing tank, the screw conveyor, and the drivemechanism for the screw conveyor, is removably mounted to the mountingopening. Therefore, the following advantageous effects are exhibited.

[0034] In the case that the cleansing tank and the screw conveyor areworn by relative movement with the filtration media, they can be removedfrom the upper portion of the filtration tank. The worn parts may bereplaced by inserting them through the upper portion of the filtrationtank. Accordingly, maintenance of the filtration apparatus isfacilitated.

[0035] A configuration may be adopted wherein the lower end of the screwconveyor protrudes from the lower opening of the cleansing tank. In thiscase, the filtration media is easily pushed upward into the cleansingtank by the lower end of the screw conveyor during cleansing. Therefore,the cleansing efficiency is improved.

[0036] A configuration may be adopted wherein the cleansing portion isconstructed by a plurality of parts, which are detachably linked so asto separate in the axial direction of the screw conveyor. In this case,even if the filtration apparatus is installed indoors in a room with alow ceiling, removal of the screw conveyor is facilitated by separatingthe cleansing portion. Accordingly, maintenance of the cleansing portionand the interior of the filtration apparatus, and replacement of thescrew conveyor and the like, can be performed without being restrictedby the installment location of the filtration apparatus.

[0037] A configuration may be adopted wherein slots that enable thefiltration media to pass therethrough are formed at the lower portion ofthe cleansing tank so that at least a portion of the slots are below theupper surface of the filtration media. In this case, the filtrationmedia easily flow into the cleansing tank through the slots. Therefore,the filtration media is easily housed within the cleansing tank as well,increasing the filtration function within the cleansing tank.

[0038] A configuration may be adopted wherein a plurality of gaps thatextend along the outer periphery of the axis of the screw conveyor areformed in the interior sides of the blades of the screw conveyor. Inthis case, the following advantageous effects are exhibited. It ispossible to reduce resistance of the filtration media, by performingbackwash cleansing during removal of the cleansing tank and the screwconveyor, thereby causing the filtration media to float. At this time,liquid enters the cleansing tank through the gaps to enter the cleansingtank, more effectively causing the filtration media to float. Therefore,removal of the cleansing tank and the screw conveyor is furtherfacilitated. In addition, back wash cleansing may be performed prior todriving a motor for the screw conveyor during cleansing. At this timealso, the motor can be driven with low resistance by causing thefiltration media to float in a similar manner.

[0039] The filtration tank may be filled with the liquid to be filteredso that the liquid surface is at least at the upper openings of thecleansing tank. In this case, the liquid enters the cleansing tankeasily, enabling active filtration to be performed within the cleansingtank.

[0040] In addition, the filtration apparatus is of a configurationwherein the mounting opening that the filtration media is visiblethrough is provided in the filtration tank above the filtration media,and a removably attachable lid is provided to cover the mountingopening. The lid is removed only during cleansing of the filtrationmedia, to insert and fix the cleansing means in the mounting opening,the cleansing means comprising the hollow cleansing tank, the screwconveyor for conveying the filtration media and the liquid upward whilescrubbing the filtration media within the cleansing tank, and the drivemechanism for the screw conveyor, to perform cleansing of the filtrationmedia. Therefore, the following advantageous effect is exhibited.

[0041] That is, the cleansing means is not necessary during normalfiltration. Therefore, the filtration apparatus may be provided at lowcost, reducing an initial investment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a sectional view of the main parts of a filtrationapparatus according to a first embodiment of the present invention.

[0043]FIG. 2 is a front view of a screw conveyor, which is utilized inthe filtration apparatus of FIG. 1.

[0044]FIG. 3 is a sectional view of the screw conveyor, taken along theline 3-3 in FIG. 2.

[0045]FIG. 4 is a sectional view of the main parts of a filtrationapparatus according to a second embodiment of the present invention.

[0046]FIG. 5 is a sectional view of the main parts of a filtrationapparatus according to a third embodiment of the present invention.

[0047]FIG. 6 is a partial magnified view of the vicinity of a mountingopening of the filtration apparatus of FIG. 5.

[0048]FIG. 7 is a sectional view of the main parts of the filtrationapparatus of FIG. 5, illustrating the process of removing a motor fromthe filtration apparatus.

[0049]FIG. 8 is a sectional view of the main parts of the filtrationapparatus of FIG. 5, illustrating the process of removing a base fromthe filtration apparatus.

[0050]FIG. 9 is a sectional view of the main parts of the filtrationapparatus of FIG. 5, illustrating the process of removing a lower shaftfrom the filtration apparatus.

[0051]FIG. 10 is a sectional view of the main parts of the filtrationapparatus of FIG. 5, illustrating the process of removing a cleansingtank from the filtration apparatus.

[0052]FIG. 11 is a sectional view of the main parts of a filtrationapparatus according to a modification of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0053] Hereinafter, the filtration apparatus of the present inventionwill be described in detail with reference to the attached drawings.FIG. 1 is a sectional view of the main parts of a filtration apparatusaccording to a first embodiment of the present invention. FIG. 2 is afront view of a screw conveyor, which is utilized in the filtrationapparatus of FIG. 1. FIG. 3 is a sectional view of the screw conveyor,taken along the line 3-3 in FIG. 2. FIG. 4 is a sectional view of themain parts of a filtration apparatus according to a second embodiment ofthe present invention.

[0054] As illustrated in FIG. 1, the filtration apparatus 1 according tothe first embodiment of the present invention comprises: a substantiallycylindrical filtration tank 2 having closed upper and lower ends; afiltration floor 4, which has a great number of fine apertures (notshown) and is provided horizontally at a lower portion of the interiorof the filtration tank 2; and a filtration media cleansing mechanism 6,which is mounted to a curved upper wall 20 of the filtration tank 2. Aplurality of supporting legs 8 (only one is shown in the figure) aremounted on the filtration tank 2. The filtration tank 2 is installed ona floor 10 via the supporting legs 8. A great number of shortcylindrical ceramic filters 12, which have fine apertures, are providedon the filtration floor 4. The filters 12 have strength to withstandfiltration media 14 that accumulates on the filtration floor 4, andwater (liquid) 16 within the filtration tank 2. The filters 12 operateto efficiently pass only purified water 16 below the filtration floor 4.

[0055] Radially extending recesses 18 are formed in the central portionof the filtration floor 4. Filters 12 are also provided within theserecesses 18, causing the height of the filters 12 at the central portionof the filtration floor 4 to be low. The reason for forming the recesses18 will be described later.

[0056] A circular mounting opening 22 is formed at the central portionof the upper wall 20 of the filtration tank 2. The filtration mediacleansing mechanism 6 is mounted in the mounting opening 22. Theperiphery of the mounting opening 22 is formed into a rim 24 formounting. A base 28, on which a motor 26 and a brake mechanism 27 aremounted, is mounted on the rim 24. A holding portion 36, which hasbearings 30 at three locations, is formed within the base 28. Thebearings 30 at the three locations rotatably support a shaft 34 of ascrew conveyor 32.

[0057] Next, the filtration cleansing mechanism 6 will be described indetail, with reference to FIG. 2 and FIG. 3 as well. A cleansing tank38, which is a cylindrical body, is provided with a discoid partitionwall 29 at the upper portion thereof. A flange 31 at the outer peripheryof the partition wall 29 is mounted onto the rim 24, and secured theretowith bolts, along with the base 28. Accordingly, it is necessary thatthe mounting opening 22 is of a size that enables the cleansing tank 38to pass therethrough. In this manner, the upper portion of the cleansingtank 38 is mounted onto the rim 24, and substantially the entirety ofthe cleansing tank 38 is suspended from the upper wall 20. An aperture33 that engages the holding portion 36 to form a seal therewith isformed in the center of the flange 31. Thereby, the interior of thefiltration tank 2 is maintained in a sealed state during filtration.

[0058] The lower portion of the cleansing tank 38 is open, to form acircular lower opening 40. A plurality of upper openings 42 that extendin the vertical direction are formed at predetermined intervals in theupper portion of the cleansing tank 38. The positional relationshipbetween the filtration media and the lower opening 40 is determined sothat the lower opening 40 is positioned within the filtration media 14.The screw conveyor 32 is provided within the interior of the cleansingtank 38. As illustrated in FIG. 1 and FIG. 2, the shaft 34 of the screwconveyor 32 comprises a reduced diameter portion 34 a and a largediameter portion 34 b. The reduced diameter portion 34 a is supported bythe bearings 30. A link portion 46, for linking the shaft 34 with themotor 26, is formed at the upper end of the shaft 34. The large diameterportion 34 b, which is provided to add strength to the shaft 34, is ahollow pipe with a closed end 44. A spiral screw blades 43 is formed onthe large diameter portion 34 b. The blade 43 is formed to the lower end44 of the shaft 34.

[0059] As shown in FIG. 3, a gap 48 is formed in the inner periphery ofthe blade 43, along the outer periphery of the shaft 34. In the presentembodiment, the gap 48 is formed continuously along the outer peripheryof the shaft 34. The blade 43 is linked to the shaft 34 by welding linkpieces 50 (supporting members) thereto at predetermined intervals. Notethat the gap 48 and the link pieces 50 are omitted from FIG. 1 and FIG.2. The gap 48 is formed continuously in the present embodiment. However,a plurality of gaps may be formed along the outer periphery of the shaft34. In this case, the link between the shaft 34 and the blade 43 maybeestablished by support members which are integrally formed with theblade 43, instead of the separate link pieces 50.

[0060] The aforementioned gap 48 (ribbon space) between the outerperiphery of the shaft 34 and the blade 43 is set to be within a rangefrom 1% to 98% of the area of the blade 43. Preferably, the gap is setto be within a range from 30% to 60%. If the gap 48 is not provided, thefiltration media 14 does not sufficiently enter the cleansing tank 38during backwash cleansing, to be described later. However, if the gap 48is excessively large, the filtration media 14 becomes difficult toconvey toward the upper portion of the cleansing tank 38 duringcleansing. Accordingly, the appropriate area ratio of the blade 43 andthe gap 48 is set as described above.

[0061] The link portion 46 at the upper end of the screw conveyor 32 islinked to the brake mechanism 27 of the motor 26 via a coupling 52. Whenthe blade 43 of the screw conveyor 32 is placed within the cleansingtank 38 in this manner, the upper end of the blade 43 is positioned inthe vicinity of the lower edges 42 a of the upper openings 42, asillustrated in FIG. 1. In addition, the lower portion 35 of the screwconveyor 32 (refer to FIG. 1) protrudes downward from the lower opening40 of the cleansing tank 38, and the lower end 44 of the shaft 34 ispositioned in the vicinity of the filtration floor 4. This configurationenables the most efficient cleansing of the filtration media 14 in thevicinity of the filtration floor 4 during cleansing of the filtrationmedia 14. The outer peripheral edge 54 of the screw conveyor 32 (referto FIG. 3) is placed so as to form a slight gap between it and the innerperipheral surface of the cleansing tank 38. The dimension of the gap isapproximately two to three times the particle diameter of the filtrationmedia 14. The gap may be larger, but the maximum allowable size of thegap is approximately 30 mm. The gap is provided to reduce thepossibility of the filtration media 14 being crushed, in the case thatthe filtration media 14 is trapped between the blade 43 and thecleansing tank 38. In other words, if the gap (clearance) is smallerthan the dimensions described above, the filtration media 14 will betrapped and crushed between the outer edge 54 of the blade 43 and theinner peripheral surface of the cleansing tank 38. This will precludethe obtainment of desired filtration function during filtration. If thegap is larger than the dimensions described above, the filtration media14 will drop through the gap, and not be discharged through the upperopenings 42 of the cleansing tank 38. That is, only the same filtrationmedia 14 will be cleansed, and the filtration media 14 to the exteriorof the cleansing tank 38 in the radial direction will not be cleansed.The manner of cleansing will be described later.

[0062] Next, the parts which are attached to the exterior of thefiltration tank 2 will be described with reference to FIG. 1. Adownwardly extending purified water discharge pipe 60 is mounted ontothe center of the curved bottom wall 58 of the filtration tank 2.Purified water, which has passed through the filtration media 14, thefiltration floor 4, and the filters 12 are discharged via the purifiedwater discharge pipe 60. A raw water filling opening 62 (contaminantexpulsion means) is positioned at the right side of the filtration tankin FIG. 1. The filtration tank 2 is filled with raw water, that is,unfiltered water 16, through the raw water filling opening 62 duringfiltration. A water level adjusting opening 64 is positioned below theraw water filling opening 62. The water level adjusting opening 64serves to optimize the water level during cleansing of the filtrationmedia 14, by expelling water 16 from the filtration tank 2 therethrough.The amount of water 16 necessary during cleansing is that which realizesfluidization of the filtration media 14 at the upper openings 42 of thecleansing tank 38. However, if the amount of water 16 is excessive, theparticle density of the filtration media 14 on the screw conveyor 32 isdecreased. The decrease in particle density decreases opportunities forthe particles to scrub against one another, thereby deteriorating thecleansing efficiency. In the present embodiment, the ratio of filtrationmedia 14 to water 16 that yields the most efficient cleansing functionis 2:1.

[0063] Reference numeral 68 in FIG. 1 denotes an inspection opening,which is utilized to inspect the state of the interior of the filtrationtank 2. An air release valve 70 is positioned on the upper wall 20 ofthe filtration tank 2, on the left side in FIG. 1. The air release valve70 enables filling of the filtration tank 2 with raw water, by expellingair within the filtration tank 2. During cleansing, the amount of rawwater is decreased. Therefore, at this time, air is caused to flow intothe filtration tank 2 from the exterior, to decrease the amount of rawwater without generating negative pressure. Reference numeral 72 denotesa filtration media filling opening.

[0064] Next, the filtration operation within the filtration tank 2 willbe described. First, the filtration tank 2 is filled with raw waterthrough the war water filling opening 62, under pressure from a pump(not shown). As the water level 74 rises, air within the filtration tank2 is expelled through the air release valve 70. In the presentembodiment, the water level 74 is set so that it rises above the rawwater filling opening 62 and reaches the upper portion of the filtrationtank 2. That is, the water level 74 is set so that substantially theentirety of the filtration tank 2 is filled with water 16 (raw water).The water level 74 illustrated in FIG. 1 is at a position prior to thefiltration tank 2 being filled with water. The water 16 permeates thefiltration media 14 in the filtration tank 2, and also enters thecleansing tank 38 via the upper openings 42, to permeate the filtrationmedia 14 within the cleansing tank 38. This enables filtration to beperformed within the cleansing tank 38 as well. The water, which haspermeated the filtration media 14 and has been filtered, is dischargedto the exterior via the purified water discharge pipe 60, provided atthe lower portion of the filtration tank 2. The purified water is thenutilized.

[0065] Next, the method of cleansing the filtration media 14, when thefiltration media 14 has been utilized over a long period of time andclogging is generated therein, will be described. Purified water isbackwashed through the purified water discharge pipe 60 prior to drivingthe motor 26 that rotates the screw conveyor 32, to cause the filtrationmedia 14 to float. Thereby, the load on the motor 26 during startup isreduced. When the motor 26 is driven, the screw conveyor 32 rotates. Thefiltration media 14 is conveyed upward to the interior of the cleansingtank 38, by the blade 43 of the rotating screw conveyor 32, particularlyby the portion of the blade 43 that protrudes below the cleansing tank38. The backwash of the purified water is continued during the initialstage of rotation of the screw conveyor 32. This is because mixing ofthe filtration media 14 at the radially outer and inner portions of thecleansing tank 38 is facilitated by rotating the screw conveyor 32 inthe backwash cleansing state, due to centrifugal force of the screwconveyor 32. At the same time, the entirety of the filtration media 14is thoroughly cleansed by this movement. The backwash of the purifiedwater is ceased thereafter. However, the rotation of the screw conveyor32 is continued to perform cleansing. The particles of the filtrationmedia 14 are conveyed upward by the rotation of the screw conveyor 32while rubbing against and scrubbing each other, and are discharged fromthe upper openings 42 into the filtration tank 2. Separation ofcontaminants from the filtration media 14 is enhanced by the impact ofthe filtration media 14 with the surface of the water 16. The filtrationmedia 14 which has dropped back into the filtration tank 2 is conveyedupwards into the cleansing tank 38 repeatedly, and scrubbed therein. Inthis manner, contaminants are separated from the filtration media 14 byrepetitive cleansing within the cleansing tank 38. As illustrated inFIG. 1, the lower end 44 of the screw conveyor 32 is positioned in thevicinity of the filtration floor 4. Therefore, the filtration media 14close to the filtration floor 4 is conveyed upward as well, therebythoroughly cleansing the entirety of the filtration media 14.

[0066] When cleansing is complete, purified water is backwashed throughthe purified water discharge pipe 60 again. The backwash cleansing iscontinued after rotation of the screw conveyor 32 is ceased.Contaminants, which have been separated from the filtration media 14,are caused to float by the backwash, and are expelled to the exteriorthrough the raw water filling opening 62, along with water that containscontaminants. The water 16 is effectively backwashed through theinterior of the cleansing tank 38 as well, by passing through the gap 48of the blade 43. Therefore, contaminants within the cleansing tank 38are expelled as well. By continuing the backwash cleansing for apredetermined amount of time, all of the contaminants within thefiltration tank 2 are removed.

[0067] Next, replacement of the cleansing tank 38 and the screw conveyor32 when they become worn will be described. The cleansing tank 38 andthe screw conveyor 32 can be extracted to the exterior of the filtrationtank 2, by removing the bolts (not shown) that fix the base 28 and therim 24 to each other, and by removing the base 28 from the rim 24. Atthis time, the blade 43 of the screw conveyor 32 is buried in thefiltration media 14. Resistance against extraction is reduced bybackwash of purified water through the purified water discharge pipe 60,thereby causing the filtration media 14 to float. In this manner, thescrew conveyor 32 and the cleansing tank 38 may be easily extracted.Only the screw conveyor 32 may be removed, according to maintenancerequirements. When the screw conveyor 32 and the cleansing tank 38 arereinstalled, backwash of purified water through the purified waterdischarge pipe 60 is performed again. This causes the filtration media14 to float, thereby reducing the resistance against insertion by thefiltration media 14. In this manner, the screw conveyor 32 and thecleansing tank 38 may be easily reinstalled.

[0068] Next, a filtration apparatus 100 according to a second embodimentof the present invention will be described with reference to FIG. 4.Note that the parts of the filtration apparatus 100 which are in commonwith those of the first embodiment will be described by using the samereference numerals. The filtration apparatus 100 differs from thefiltration apparatus 1 of the first embodiment in that a cleansing tank138 extends downward longer than the cleansing tank 38, and a pluralityof slots 176 are provided therein. The slots 176 extend vertically, andare provided at the lower portion of the cleansing tank 138 at intervalsalong the circumferential direction thereof. The vertical length of theblade 43, which is housed within the cleansing tank 138, can beextended, due to the extended length of the cleansing tank 138. Thecleansing function is improved by this configuration, because thedistance, over which the filtration media 14 is scrubbed, is increased.

[0069] The slots 176 are formed to be of a size that allows theparticles of the filtration media 14 to pass therethrough. The slots 176facilitate entry of the filtration media 14 into the cleansing tank 138.The slots 176 may be of any desired shape, such as elongated in thehorizontal direction. Entry of the filtration media 14 into thecleansing tank 13 may be further facilitated, by setting a positionalrelationship in which the height of the upper edges 176 a of the slots176 are above the upper surface 66 of the filtration media 14.

[0070] Next, a filtration apparatus 200 according to a third embodimentof the present invention will be described with reference to FIG. 5.FIG. 5 is a sectional view of the main parts of the filtration apparatus200 according to the third embodiment of the present invention. Thefiltration apparatus 200 differs from the filtration apparatuses of thefirst and second embodiments in that the screw conveyor is separableinto a plurality of parts. Thereby, assembly and disassembly of thefiltration apparatus is enabled within a space having a small verticalheight. Note that in the following description, the parts of thefiltration apparatus 200 which are in common with those of the previousembodiments will be described by using the same reference numerals.

[0071] As illustrated in FIG. 5, the filtration apparatus 200 comprisessupport legs 208, and a filtration tank 202. The filtration tank 202 isof a larger dimension in the vertical direction than those of theprevious two embodiments. A filtration floor 204, which is similar tothat of the previous embodiments, is provided at the lower portion ofthe filtration tank 202. A plurality of filters 12 are provided on thefiltration floor 204, as in the previous embodiments. A base 228, onwhich a motor 226 and a brake mechanism 227 are mounted, is mounted on arim 224 of the upper wall 220 of the filtration tank 202. The base 228is of a similar construction as those of the previous two embodiments,and comprises a holding portion 236 (236 a and 236 b), which isseparable in the vertical direction, for holding a screw conveyor 232.The details of the base 228 and the holding portion 236 will bedescribed later.

[0072] A cylindrical cleansing tank 238 and the screw conveyor 232 areplaced in a mounting opening 222 formed by the rim 224. The cleansingtank 238 is longer than those of the previous two embodiments, and thescrew conveyor 232 protrudes downwardly through a lower opening 240 ofthe cleansing tank 238.

[0073] Next, the screw conveyor 232, the cleansing tank 238, and thebase 228 will be described in further detail, with combined reference toFIG. 6. FIG. 6 is a partial magnified view of the vicinity of themounting opening 222. The mounting opening 222 is formed by the annularrim 224 being welded to the upper end of the filtration tank 202. Therim 224 comprises an upwardly facing step 278 at its inner periphery.Meanwhile, a flange 237 is welded to the outer periphery of the upperend of the cylindrical cleansing tank 238.

[0074] A downwardly facing annular step 280, which is complementary tothe step 278 of the rim 224, is formed at the outer periphery of theflange 237. The steps 278 and 280 are configured such that the step 280is seated on the step 278 when the cleansing tank 238 is inserted intothe mounting opening 222 from above. The steps 278 and 280 are fixed toeach other by a plurality of bolts 282, which are provided along thecircumferential direction thereof. In this manner, the cleansing tank238 is removably attached to the filtration tank 202. Note that in thefigures, only a portion of the bolts 282 is illustrated. As illustratedin FIG. 5, the lower opening 240 of the cleansing tank 238 is positionedabove the filtration floor 204. That is, a gap exists between the loweropening 240 and the filtration floor 204. The lower end 235 of the screwconveyor 232 protrudes from the lower opening 240, to be positionedwithin this space. Note that the screw conveyor 232 will be described indetail later.

[0075] Next, the base 228 will be described with reference to FIG. 5 andFIG. 6. The base 228 comprises an upper base 228 a and a lower base 228b (refer to FIG. 6). The upper base 228 a comprises a cylindrical member284 a, an annular member 286 a, and an annular member 286 b. The annularmembers 286 a and 286 b are welded to the upper and lower ends of thecylindrical member 284 a, respectively. The upper annular member 286 a,the lower annular member 286 b, and the cylindrical member 284 a arereinforced by a plurality of reinforcement ribs 288 a, which areprovided along the circumferential direction and welded perpendicularlythereto. The lower base 228 b comprises a cylindrical member 284 b, anannular member 286 c (partition wall), and an annular member 286 d(partition wall) The cylindrical member 284 b has a shorter dimension inthe vertical direction than the cylindrical member 284 a. The annularmembers 286 c and 286 d are welded to the upper and lower ends of thecylindrical member 284 b, respectively. The annular member 286 c, theannular member 286 d, and the cylindrical member 284 b are reinforced bya plurality of reinforcement ribs 288 b, which are provided along thecircumferential direction and welded perpendicularly thereto.

[0076] The upper base 228 a and the lower base 228 b are linked by aplurality of sets of bolts 290 and nuts 291, which are provided alongthe circumferential direction of the annular members 286 b and 286 c,thereby constructing the integrated base 228. The base 228 is mounted tothe filtration tank 202 by the annular member 286 d being fixed to therim 224 with the plurality of bolts 292, which are provided along thecircumferential direction of the rim 224. That is, the annular member286 d is mounted to the filtration tank 202 by the bolts 292, at aflange portion that protrudes outward from the outer periphery of thecylindrical member 284 b. Note that a channel 287 is provided within theannular member 286 d so as to communicate the interior and the exteriorof the cylindrical member 284 b. The channel 287 serves as a drain forexpelling water that enters the cylindrical member 286 d.

[0077] Referring again to FIG. 5, the motor 226 and the brake mechanism227, which is integral with the motor 226, are mounted on the base 228,which is mounted on the filtration tank 202 in this manner, with bolts(not shown). A rotating shaft 293 of the brake mechanism 227 and a shaft234 of the screw conveyor 232 are linked via a coupling 252.

[0078] Next, the screw conveyor 232 and a support structure thereforwill be described. As illustrated in FIG. 5, the screw conveyor 232comprises an upper shaft 234 a and a lower shaft 234 b. The upper shaft234 a is held by the holding portion 236. The lower shaft 234 b isdetachably linked to the upper shaft 234 a. The screw conveyor 232differs from those of the previous two embodiments in that the uppershaft 234 a and the lower shaft 234 b are separable at a separatingportion 294. The separating portion 294 enables separation of the upperand lower shafts 234 a and 234 b, by linking the two at flanges 294 aand 294 b with bolts 295. The flange 294 a is formed at the lower end ofthe upper shaft 234 a, and the flange 294 b is formed at the upper andof the lower shaft 234 b. The reason that the screw conveyor 232 isprovided to be separable will be described later. A spiral blade 243 isformed on the screw conveyor 232 to the lower end 244 of the shaft 234,in a similar manner to those of the previous two embodiments. Theseparating portion 294 is provided at a portion of the shaft 234 wherethe blade 243 is not formed, in the vicinity of the upper end of theblade 243. This is in order to secure as long a dimension as possiblefor the blade 243, while effectively reducing the dimensions of theshaft 234 after separation. As a result, the separating portion 294 ispositioned in the vicinity of the upper ends of upper openings 242 ofthe cleansing tank 238.

[0079] Next, the holding portion 236 will be described with reference toFIG. 5 and FIG. 6. The upper holding portion 236 a comprises acylindrical main body 298 and tapered roller bearings 296 at the upperand lower ends thereof. The tapered roller bearings 296 rotatably holdthe upper shaft 234 a of the shaft 234 in a vertical orientation. Thetapered roller bearings 296 are provided within recesses 298 a, whichare formed in the upper and lower ends of the main body 298. Annularplates 300 are fixed to the upper and lower ends of the main body 298with screws 302. The annular plates 300 serve to prevent extraction ofthe tapered roller bearings 296. A plurality of vertically extendingribs 304 are welded along the outer periphery of the main body 298. Eachof the ribs 304 has a horizontally fixing piece 306 at the lower endthereof. The fixing pieces 306 are fixed to the annular member 286 cwith bolts 308. In this manner, the upper holding portion 236 a is fixedto the lower base 228 b.

[0080] Next, the lower holding portion 236 b will be described. Acircular aperture 333 for housing the lower holding portion 236 b isformed in the annular member 286 d. The lower holding portion 236 bcomprises a cylindrical main body 312 that extends in the axialdirection of the upper holding portion 236 a. The lower holding portion236 b is placed within the aperture 333 and fixed thereto by welding. Atthe same time, ribs 314 are welded to the main body 312 and the annularmember 236 d, to strengthen the link between the main body 312 and theannular member 286 d. Packing material 316 is provided between the mainbody 312 and the shaft 234, in the upper portion of the main body 312.The packing material 316 is held by a cylindrical stop 318 of anextraction preventing member 320. The extraction preventing member 320is fixed to the annular member 286 d with screws 322, which are held ina flange 319 that protrudes from the stop 318. A bearing 326 is providedin a space 324 at the lower portion of the main body 312. An oil seal328 is provided below the bearing 326. A discoid plate 332 having anopening 330 formed therein is provided below the oil seal 328. Thediscoid plate 332 serves to prevent extraction of the oil seal 328. Theshaft 234 penetrates the opening 330, and the discoid plate 332 is fixedto the main body 312 with screws 334.

[0081] There are cases in which the filtration apparatus 200, which isconstructed in the manner described above, is installed and utilizedindoors. After a predetermined period of use in this utilization state,it becomes necessary to perform maintenance and replacement of the screwconveyor 232 and the like, which become worn. The steps involved in thedisassembly process of the filtration apparatus 200 for maintenanceoperations will be described with reference to FIG. 7 through FIG. 10.FIG. 7 is a sectional view of the main parts of the filtration apparatus200, illustrating the process of removing the motor 226 therefrom. FIG.8 is a sectional view of the main parts of the filtration apparatus 200,illustrating the process of removing the base 228 therefrom. FIG. 9 is asectional view of the main parts of the filtration apparatus 200,illustrating the process of removing the lower shaft 234 b therefrom.FIG. 10 is a sectional view of the main parts of the filtrationapparatus 200, illustrating the process of removing the cleansing tank238 therefrom.

[0082] First, a description will be given with reference to FIG. 7. Themotor 226 is removed from the base 228 as indicated by arrow A, byremoving the bolts (not shown) that fix the motor 226 to the vase 228.At this time, the coupling 252 is prepared for separation, by removing abolt (not shown) in advance.

[0083] Next, as illustrated in FIG. 8, the bolts 292 (refer to FIG. 6)that fix the base to the rim 224 are removed. Then, the base issuspended by a hook 346 engaging a rope or a wire 344, which is fedthrough eye bolts 342. The hook 346 is provided as part of a conveyanceapparatus 340 (geared trolley), which is mounted on a rail 338 of theceiling 336 of a building. At this time, the screw conveyor 232, whichis held by the holding portion 236, is also drawn upward. However, thescrew conveyor 232 cannot be completely extracted, due to therelationship between the length thereof and the height of the ceiling.Therefore, a temporary base 348 is mounted on the rim 224 after thescrew conveyor 232 is drawn out to a predetermined height. The screwconveyor 232 is temporarily placed on the temporary base 348. The flange294 b of the separating portion 294 of the shaft 234 is placed on thetemporary base 348.

[0084] The temporary base 348 is configured to be separable in thedirection perpendicular to the axial direction of the shaft 234. Whenassembled, an opening 350 for receiving the shaft 234 is formed in theupper portion of the temporary base 348. The flange 294 b is placed onthe peripheral edge of the opening 350. It is preferable that thetemporary base 348 is a cylindrical member. The cylindrical temporarybase 348 is constituted of two parts, and is provided on the rim 224from both sides of the shaft 234. The temporary base 348 may beconstructed from a plurality of members having legs that abut the rim224, as an alternative to the cylindrical construction.

[0085] After the base 228 is placed on the temporary base 348, the bolts295 that link the separating portion 294, thereby separating the uppershaft 234 a from the lower shaft 234 b. In this manner, the base 228 andthe upper shaft 234 a are enabled to be moved horizontally in thedirection indicated by arrow B, without lifting them any higher. At thistime, the lower shaft 234 b is left in a state in which it is supportedby the temporary base 348.

[0086] Then, as illustrated in FIG. 9, the lower shaft 234 b is liftedand removed from the cleansing tank 238 by the conveyance apparatus 340or the like, at the same time that the temporary base 348 is removedfrom the rim 224.

[0087] Thereafter, as illustrated in FIG. 10, the bolts 282 that fix thecleansing tank 238 to the rim 224 are removed, and the cleansing tank238 is extracted upward from the mounting opening 222.

[0088] In this manner, it is possible to sequentially remove each partfrom the mounting opening 222 of the filtration tank 202 when performingmaintenance operations. This enables extremely efficient operations.Particularly, because the screw conveyor 232 is of a separablestructure, the operations can be performed even indoors, with arelatively low ceiling. Note that the manner in which filtration andfiltration media cleansing is performed is the same as those of theprevious two embodiments.

[0089] As described above, in the third embodiment, the shaft 234 is ofa separable structure, which yields good maintenance properties.Therefore, an advantageous effect is exhibited in that a cleansing tank202 having good filtration efficiencies, by virtue of being long in thevertical direction, may be utilized even indoors, with a relatively lowceiling.

[0090] The preferred embodiments of the present invention have beendescribed in detail above. However, the present invention is not limitedto the configurations described above. For example, the lower ends 44and 244 of the screw conveyors 32 and 232 are free ends. However, aconfiguration may be adopted wherein the lower ends 44 and 244 aresupported. Specifically, the lower ends 44 and 244 maybe conical inshape, and a member having a recess for receiving the tip of the conemay be provided on the filtration floors 4 and 204. By thisconfiguration, horizontal displacement of the screw conveyors 32 and 232may be further suppressed. In addition, this configuration poses noobstacles to the replacement of the screw conveyors 32 and 232, and thecleansing tanks 38, 138, and 238.

[0091] In addition, the screw conveyors 32 and 232 are capable ofconveying the filtration media 14 upward without necessarily protrudingdownward beyond the cleansing tanks 38, 138, and 238. In this case, thefiltration media 14 is enabled to enter the cleansing tanks 38, 138, and238 with relatively lower resistance by providing the lower ends 44 and244 of the screw conveyors 32 and 232 above the filtration floors 4 and204 at a distance.

[0092] It is preferable that the positions of the upper openings 42 arenot too low. This is to enable scrubbing of the filtration media 14 overa longer distance within the cleansing tanks 38, 138, and 238. Inaddition, the manner of attachment between the cleansing tanks 38, 138,and 238 and the mounting openings are not limited to those of theembodiments described above. Various constructions may be consideredthat enable easy assembly and disassembly.

[0093] Note that in the above embodiments, cases in which water isfiltered were described. However, the filtration apparatus of thepresent invention may be utilized to filter liquids other than water,such as oil.

[0094] Further, the cleansing portion includes the cleansing tanks 38,138, and 238, the screw conveyors 32 and 232, and the drive mechanismsfor the screw conveyors 32 and 232. However, the motors 26 and 226 arenot necessarily included. In the case that the motors 26 and 226 are notincluded, they may be directly provided on the filtration tanks 2 and202. In this case, the rotation of the motors is transferred to thescrew conveyors via link portions. When the drive portions and themotors 26 and 226 are disassembled, the disassembly may be performed atthe link portions.

[0095] Next, a modification of the present invention will be describedwith reference to FIG. 11. FIG. 11 is a sectional view of the main partsof a filtration apparatus 400 according to a modification of the presentinvention, in which a cleansing portion and a filtration tank are shownseparately. The filtration apparatus 400 comprises a filtration tank402, which is similar to the filtration tank 2. The filtration tank 402comprises: a raw water filling opening 462; two filtration floors 404and 407, which are separated in the vertical direction; strainers 412,which are provided on the lower filtration floor 404; a purified waterdischarge pipe 460 for discharging filtered water; and an air releasevalve 470. Two filtration floors are provided in the filtrationapparatus 400. Filtration media 414 is housed above the upper filtrationfloor 407, and filtration media 454 is housed between the lowerfiltration floor 404 and the upper filtration floor 407.

[0096] A circular mounting opening 422 is formed at the center of theupper wall 420 of the filtration tank 402. A cleansing portion 403(cleansing means), which is shown to the right of the filtration tank402 separated therefrom, is mounted on the mounting opening 422. Theperipheral edge of the mounting opening 422 is formed into a mountingrim 424. A discoid lid 405 is fixed on the rim 424 by a plurality ofbolts 492, which are provided at predetermined intervals along the rim424. In this manner, the mounting opening 422 is closed by the lid 405during filtration. Accordingly, the filtration apparatus 400 does notcomprise the cleansing portion 403 during filtration.

[0097] When the filtration apparatus 400 is utilized to filter water 416(liquid), the filtration tank 402 is filled with the water 416 throughthe raw water filling opening 462. The raw water 416 is filtered bypassing through the filtration media 414 and 454, then filtered water isdischarged through the purified water discharge pipe 460.

[0098] Next, the cleansing portion 403 will be described. The cleansingportion 403 is of a similar construction to the cleansing portions ofthe filtration apparatuses 1, 100, and 200 illustrated in FIG. 1, FIG.4, and FIG. 7. The cleansing portion 403 comprises: a motor 426 (driveportion); a brake mechanism 427 (drive portion) for decelerating therotation of the motor 426; and a base 428 for supporting the motor 426and the brake mechanism 427. A cylindrical cleansing tank 438 is mountedon the base 428. A screw conveyor 432, which is linked to the brakemechanism 427 via a coupling 452 and which is rotated by the motor 426,is provided within the cleansing tank 438. The base 428 of the cleansingportion 403 further comprises a flange 409 for mounting onto the rim424. Apertures (not shown) are formed in the flange 409, at the sameintervals as those of the bolts in the lid 405.

[0099] Next, a case in which the filtration media 414 and 454, whichhave contaminants trapped therein after a predetermined period of use,are cleansed, will be described. First, the lid 405 is removed, and themounting opening 422 is exposed. Then, the cleansing tank 438 of thecleansing portion 403 is inserted through the mounting opening 422. Theflange 409 of the cleanisng portion 403 is placed on the rim 424 andbolted thereto, to fix the cleansing portion 403 to the filtration tank402. Thereafter, the cleansing portion 403 is operated as in theprevious embodiments, and the filtration media 414 is cleansed. Notethat in FIG. 11, reference numeral 471 denotes an ultrasonic wavegenerating apparatus that separates contaminants from the filtrationmedia 454 with ultrasonic vibrations.

[0100] The cleansing operation performed by the cleansing portion 403 issimilar to those of the previous embodiments, and a rough descriptionthereof is as follows. First, backwash of purified water is performedthrough the purified water discharge pipe 460 to cause the filtrationmedia 414 to float, prior to driving the motor 426 that rotates thescrew conveyor 432. Thereby, the load on the motor 426 during startup isreduced. When the motor 426 is driven, the screw conveyor 432 rotates.The filtration media 414 is conveyed upward to the interior of thecleansing tank 438, by a blade 443 of the rotating screw conveyor 432,particularly by the portion of the blade 443 that protrudes below thecleansing tank 438. The backwash of the purified water is continuedduring the initial stage of rotation of the screw conveyor 432. This isbecause mixing of the filtration media 414 at the radially outer andinner portions of the cleansing tank 438 is facilitated by rotating thescrew conveyor 432 in the backwash cleansing state, due to centrifugalforce of the screw conveyor 432. At the same time, the entirety of thefiltration media 414 is thoroughly cleansed by this movement. Thebackwash of the purified water is ceased thereafter. However, therotation of the screw conveyor 432 is continued for a short timethereafter, to perform cleansing.

[0101] The particles of the filtration media 414 are conveyed upward bythe rotation of the screw conveyor 432 while rubbing against andscrubbing each other, and are discharged from upper openings 442 of thecleansing tank 438 into the filtration tank 402. Separation ofcontaminants from the filtration media 414 is enhanced by the impact ofthe filtration media 414 with the surface of the water 416. Thefiltration media 414 which has dropped back into the filtration tank 402is conveyed upwards into the cleansing tank 438 repeatedly, and scrubbedtherein. In this manner, contaminants are separated from the filtrationmedia 414 by repetitive cleansing within the cleansing tank 438. At thistime, contaminants within the filtration media 454 may be effectivelyremoved by vibrations generated by the ultrasonic wave generatingapparatus 471. As illustrated in FIG. 11, the lower end 444 of the screwconveyor 432 is positioned in the vicinity of the filtration floor 407.Therefore, the filtration media 414 close to the filtration floor 407 isconveyed upward as well, thereby thoroughly cleansing the entirety ofthe filtration media 414, in a similar manner as in the previousembodiments.

[0102] When cleansing is complete, purified water is backwashed throughthe purified water discharge pipe 460 again. The backwash cleansing iscontinued after rotation of the screw conveyor 432 is ceased.Contaminants, which have been separated from the filtration media 414,are caused to float by the backwash, and are expelled to the exteriorthrough the raw water filling opening 462, along with water thatcontains contaminants. By continuing the backwash cleansing for apredetermined amount of time, all of the contaminants within thefiltration tank 402 are removed.

[0103] When the cleansing and rinsing of the filtration media 414 and454 are complete, the cleansing portion 403 is removed, the lid 405 ismounted on the rim 424, and the mounting opening 422 is closed. In thismanner, the filtration apparatus 400, which does not comprise thecleansing portion 403, is suited for a manner of use in which cleansingis performed only during annual maintenance, for example. As thecleansing portion 403 is unnecessary at the time of initial installment,the filtration apparatus 400 may be provided at low cost.

1. A filtration apparatus for filtering liquid, which is introduced intoa filtration tank, and discharging filtered liquid to the exterior ofthe filtration tank, comprising: the filtration tank that housesfiltration media; and a filtration media cleansing mechanism thatcomprises a hollow cleansing tank for cleansing the filtration media;and a contaminant expulsion means for expelling contaminants separatedfrom the filtration media to the exterior to the filtration tank;wherein: the cleansing tank is a cylindrical body that hangs within thefiltration tank from the upper portion thereof; the cleansing tank isprovided with a lower opening at a position lower than the upper surfaceof the filtration media housed in the filtration tank, and a pluralityof upper openings at a position higher than the upper surface of thefiltration media; the cleansing tank is provided with a screw conveyorfor conveying the filtration media and the liquid, which enter thecleansing tank from the filtration tank via the lower opening, upwardfrom the lower opening to the upper openings while scrubbing thefiltration media within the cleansing tank; a mounting opening, to whichthe upper portion of the cleansing tank is removably attachable, isprovided at the upper portion of the filtration tank; and a cleansingportion, comprising the cleansing tank, the screw conveyor, and a drivemechanism for the screw conveyor, is removably attachable to thefiltration tank via the mounting opening, from the exterior of thefiltration tank.
 2. A filtration apparatus as defined in claim 1,wherein: the lower end of the screw conveyor protrudes downward from thelower opening of the cleansing tank.
 3. A filtration apparatus asdefined in either of claim 1 or claim 2, wherein: the cleansing portionis constructed by a plurality of parts, which are detachably linked soas to separate in the axial direction of the screw conveyor.
 4. Afiltration apparatus as defined in any one of claims 1 through 3,wherein: slots that enable the filtration media to pass therethrough areformed at the lower portion of the cleansing tank so that at least aportion of the slots are below the upper surface of the filtrationmedia.
 5. A filtration apparatus as defined in anyone of claims 1through 4, wherein; a plurality of gaps that extend along the outerperiphery of the axis of the screw conveyor are formed in the interiorsides of the blades of the screw conveyor.
 6. A filtration apparatus asdefined in anyone of claims 1 through 5, wherein: the filtration tank isfilled with the liquid to be filtered so that the liquid surface is atleast at the upper openings of the cleansing tank.
 7. A filtrationapparatus for filtering liquid, which is introduced into a filtrationtank that houses filtration media, and discharges filtered liquid to theexterior of the filtration tank, wherein: a mounting opening that thefiltration media is visible through is provided in the filtration tankabove the filtration media; a removably attachable lid is provided tocover the mounting opening; and the lid is removed during cleansing ofthe filtration media, to insert and fix a cleansing means in themounting opening, the cleansing means comprising a hollow cleansingtank, a screw conveyor for conveying the filtration media and the liquidupward while scrubbing the filtration media within the cleansing tank,and a drive mechanism for the screw conveyor, to perform cleansing ofthe filtration media.